Process for generating sodium monoxide



Oct. 8, 1957 HULSE PROCESS FOR GENERATING SODIUM MONOXIDE Filed Sept.10, 1953 IN VENTOR ROBERT E. HULSE ATTORNEY Distillers and ChemicalCorporation, a corporation of Virginia Application September. 10,1953,Serial No. 379,427

2 Claims. (Cl. 23--184) This invention is a new and useful process forthe generationof sodium monoxide and is a. continuation-inpart of myprior application, now abandoned, Serial No. 274,927 filed March 5,1952. The invention will befully understood from the followingdescription read in conjunction with the drawing, which is adiagrammatic showing of apparatus in which my invention may be carriedinto effect.

In the ordinary process for the manufacture of sodium monoxide, metallicsodium is added continuously or inter mittently to amass of sodiummonoxide maintained in an oxidizing atmosphere at a temperature between130 and 400 C. The sodium is present in minor amounts, ordinarily from1-5 of the total, and the sodium monoxide functions as a diluent todisseminate the sodium, improve contact between it and the oxidizingagent, and to provide heat ballast. In this process it is diff cult toobtain complete oxidation of the sodium and-the product ordinarilycontains considerable very fine materialwhich, in the ultimateutilization of the sodium monoxide, is apt to be both disagreeable anddangerous.

One object of my invention is to oxidize the sodium quantitatively andeasily to sodiummonoxide. Another objective is to produce a productwithin any desired range of particle sizes which shall be free-flowingand also free fromdust.

in the first stage of my invention I maintain a mass of sodium monoxide,in the form of particles, in a state of continuous movement and/ oragitation in an atmosphere substantially free from oxygen and inert withrespect to both sodium monoxide and sodium. Any of the inert gases ormixtures thereof will function as inert atmosphere. The preferred gas isnitrogen. As commercially produced this contains traces of oxygen.Amounts of oxygen ranging up to one mol percent can be tolerated,although I prefer to work with an atmosphere containing not overone-half mol percent. Within these limits the sodium functions as a truemetal with sufiicient interfacial tension or wetting action to form asurface film on the particles of monoxide. With increasing amounts ofoxygen above these limits, oxidation proceeds actively and theinterfacial tension or wetting action is negatived by the development ofan oxide film covering the sodium. During this stage the temperature ismaintained at a point above the melting point of sodium and preferablybelow 250 C. To the mass of sodium monoxide particles in said inertatmosphere I add sodium to the extent of a minor part by weight of thesodium monoxide, i. e., from 1-10% and preferably from 35% by weight ofthe sodium monoxide. At this temperature and under these conditions thesodium disseminates uniformly throughout the mass of sodium monoxide,superficially wetting the individual particles and forming a film ofelemental sodium surrounding each particle. Within this temperaturerange the filming of the elemental sodium upon the particles of sodiummonoxide will ordinarily be. fully completed within a period of from30-45 minutes- All of the sodium may be added initially or the sodiummay be ire Estates Patent fit 2,809,096 Patented Oct. 8, 1957 2 addedgradually during this period or during the initial stages thereof.

Whenever the. sodium has, become uniformly and sub stantially entirelydistributed as a film. upon the particles of sodium. monoxide, theinert, atmosphere. is replaced with anoxygen-containing gas which may beeither air or air enriched withioxygenor relatively pure oxygen. Theatmosphere operates tooxidize the superficial film. of elemental sodiumuniformly and completely. to sodium monoxide. It will, then be presentas a surface layer of sodium monoxide surrounding the original particle.During the oxidation stage I prefer to maintain a temperature between200 and 300 C. and since the oxidation is exothermic, it willbenecessary to coolthe, system in some way to abstract the. excess heat.ElementaLsodium isv not added duringthe oxidation stage. The oxidizingatmosphere is replenishedand maintaineduntil at least the major part,and preferably substantially all of the sodium, is oxidized to monoxide.

The two stages are-preferablycarried out continuously, i. e., by thecontinued addition of sodium to a mass, of sodium monoxide particles in.a condition of motion or agitation, in. an'inert atmosphere, and. by thecontinuous abstraction from said mass of sodium monoxide particleswetted with. a superficial film of metallic sodium, which particles arecontinuously introduced into a second mass composedof sodiummonoxideparticles andsodium, present as asuperficial film upon these particles,in an oxidizing atmosphere, with the result that the sodium isundergoing continuous oxidation to sodium monoxide. As stated, thetemperature in the first stage is preferably below 250 C. and in thesecond stage. preferably between 200 and 300 C. (Preferably thesestages. are: operated in combination as a unitary continuous process.)Bot first. and secondstages are preferably operated at constant volume;any excess of particles over that necessary to maintain this volume iscontinuously abstracted from the second stage, apart of the same iswithdrawn from the system for commercial utilization while the remainderis recycled to the first stage to again function as a carrier forsodium. If the second stageis operated at a higher temperature than thefirst stage, the particles may be cooledin transit, so that they arriveat thefirst stage atthe proper filming. temperature.

Inthis way it is possible to build up particles of sodium monoxide ofsubstantially any desired size which, because of their mode offormation, are free from dust and relatively pure. Because of theirmethod of formation, the particles so formed have a pearl-like structureand are composed of successively formed layers of sodium monoxide. Inthe preferred method of operation the sodium monoxide particlesresulting from the second stage are classified, with the result that aparticular range of particles most suitable for utilization in otherindustries, is separated and withdrawn. This cut will be composed ofrounded particles which are free-flowing and substantially free fromdust. The over-size from the classifying operation is preferablyreground and, together with the under-size, is returned to the firststage, to be again built up into particles Qff the optimum .size. forcommercial utilization.

Referring to the drawing 1 designates, a reactor of the rotary typeprovided with circular rims 2. and 3 rotatably carried by flangedwheels, such as 4 and 5. Suitable provision is made for driving at leastsome of the wheels to rotate the reactor. Suitable provision (not.shown) is also. made for heating the reactor, if desired, to initiatereaction. Inasmuch as the reaction to be carried out in the reactor isexothermic in character, provision is also made for abstracting theexcess heat to keep the reactants down to the desired operatingtemperature, and this provision is diagrammatically indicated by pipe61:011-

trolled by valve 7 discharging into shower head 8. Material may beintroduced to the reactor through pipe 11 controlled by valve 12discharging into conveyor 13 consisting of worm 14 driven by anysuitable means diagrammatically indicated by 15 and housed in pipe 16which extends into the interior of the reactor. Pipe 16 is in turnsurrounded by pipe 17. The space between the exterior of pipe 16 and theinterior of pipe 17 forms an annular duct extending into the interior ofthe reactor and is connected to pipe 18 controlled by valve 19. Thespace between the exterior of pipe 17, which is stationary, and the end21 of reactor 1, which is rotatable, is sealed by stuffing box 22.

At the other end of the reactor conveyor 23 extends to a point withinreactor 1. This consists of worm 24 driven by any suitable meansdiagrammatically indicated by 25 and housed in pipe 26 which extends toa point within the reactor terminating in trough 27. Pipe 26 issurrounded by pipe 28. The space between pipes 26 and 28 forms anannular duct extending into the interior of the reactor and communicateswith pipe 31 controlled by valve 32. The end 33 of the reactor carrieslifts, such as 34, adapted during rotation of the reactor, to liftmaterial contained therein, and discharges into the open top of trough27, so that it may be withdrawn from the reactor by the operation ofworm 24. Material so withdrawn may be discharged through pipe 35discharging into vibrating screens 36. Of these the topmost screen 37 ispreferably about 20 mesh. The material retained on this screen isdiverted through pipe 38 to grinder diagrammatically indicated by 39.Material passing through screen 37 is discharged onto screen 41, whichis preferably about 40 mesh. The material retained on screen 41 whichwill be 20-40 mesh is discharged through chute 42 into tank 43. Materialpassing through screen 41 which will be finer than 40 mesh is caught inpan 44 and discharged thence through tube 45 into pipe 46. The grinder39 is operated to yield a product which will pass 40 mesh and thecombined products from grinder 39 and pan 44 are picked up andtransported by enclosed conveyor 47 which may be of the so-called Redlertype. Provision is made for cooling material transported by thisconveyor diagrammatically indicated by pipe 49 controlled by valve 50discharging through shower head 51 by which coolant may be distributedover the outer surface of the conveyor housing.

The Redler conveyor 47 discharges through pipe 52 into mixer 53, whichis of the enclosed type, consisting of tank 54 provided with cover 55and provided also with a mixer bar 56 driven by any suitable meansdiagrammatically indicated by 57. Provision is made for the controlledintroduction of sodium into the tank 54 from tank 61 through pipe 62controlled by valve 63. Any excess of material within the tank 54 overthat necessary to maintain level 64 will automatically flow off throughpipe 65 discharging into pipe 11.

Provision is made for operating the mixer under a controlled atmosphereand to this end a gas, such as nitrogen, may be introduced through pipe66 controlled by valve 67 passing through the mixer and thencecountercurrent to the incoming material in conveyor 47 and thence out ofthe system through pipe 68 controlled by valve 69.

Material in the mixer 53 may be held at any predetermined temperature byindirect heat exchange with a liquid circulated through jacket 70.Material may be introduced into mixer 53 when desired through pipe 71controlled by valve 72.

When starting up the system mixer 53 is purged with nitrogen fed throughpipe 66 and exhausted through pipe 68. Reactor 1 is purged with dry airthrough pipe 31 and exhausted through pipe 18. Sodium monoxide is thenintroduced into mixer 53 through pipe -71 by opening valve 72. Thetemperature of mixer 53 is brought up to 130-200 C. by circulation of asuitable hot liquid 4 in jacket 70. Reactor 1 is brought up to 200300C., preferably 200250 C., by indirect heating, usually oil or gas-fired.

Sodium is added from tank 61 through pipe 62 to the extent of about 35%of the sodium monoxide coming into the mixer through pipe 71. Duringthis stage the mixer bar 56 is continuously operated and the inert gasis continuously supplied through pipe 66 so that the mixing is at alltimes conducted in an inertatmosphere and no oxidation of the sodiumoccurs. The result of this procedure is to cause the sodium todistribute itself uniformly over the particles of sodium monoxide in themixer, forming a thin film of elemental sodium over the surface of eachsuch particle. The supply of sodium and sodium monoxide is continued inthis manner, and when the amount of sodium monoxide carrying the surfacefilm of elemental sodium has accumulated in mixer 53 in excess of thatnecessary to maintain level 64, the excess moves continuously throughpipe 65 into pipe 11, from which it is forced by conveyor 13 intoreactor 1.

Reactor 1 is kept in slow rotation. By the application of heat orcoolant, the contents are held at a temperature broadly within the rangeof 400 C., usually within the range of ZOO-300 C. and preferably Withinthe range of ZOO-250 C. An oxidizing gas, such as air or air enriched inoxygen, or relatively pure oxygen, is passed in through pipe 31. If thegas contains nitrogen, the exhausted residue consisting principally ofnitrogen, is withdrawn through pipe 18. Sodium monoxide carrying thesuperficial film of sodium is supplied to the reactor from mixer 53 atsuch a rate that the average dwell in the reactor is approximately 1-2hours. The oxidizing gas is supplied at such a rate as to provide anexcess of oxygen over that stoichiometrically corresponding to thesodium introduced during the same period. As a result of the foregoingthe film of sodium introduced into the reactor 1 as a surface filmsurrounding the particles of sodium monoxide, is substantially alloxidized to form a surface layer of sodium monoxide surrounding theoriginal particle. Sodium monoxide is continuously removed from reactor1 by conveyor 23 discharging into pipe 35. Particles which areover-size, i. e., over 20 mesh, are retained on screen 37 and divertedthrough tube 38 to grinder 39 by which they are reduced to below 40 meshand fed into pipe 46. Of the particles passing through screen 37 andwhich are minus 20 mesh, the particles above 40 mesh are retained onscreen 41 and diverted through pipe 42 into tank 43. These particleswhich will fall within the range of 20-40 mesh are freeflowing andsubstantially free from dust. The particles passing through screen 41and which are minus 40 mesh are diverted from pan 44 through tube 45into the pipe 46, by which together with the particles from grinder 39,they are transferred by the conveyor 47 back into the mixer 53. They arecooled en route by water or other suitable coolant spread over conveyor47 from the shower head 51, and thereby brought down to the temperatureobtaining in mixer 53. As soon as sodium monoxide arrives at mixer 53from Redler conveyor 47, the supply of sodium monoxide particles throughpipe 71 is discontinued and the system is thereafter continued inoperation, adding sodium to the extent of 35% of the incoming sodiummonoxide from conveyor 47 and abstracting particles of sodium monoxideof from 20-40 mesh through pipe 42. Because the particles generated inthe operation of the process are built up by the formation of successivelayers of sodium monoxide, they are freefiowing and free from dust.While I have described abstracting a cut of such particles of from 2040mesh, it will of course be understood that in commercial practice therange of particle sizes abstracted will be that required by the market.The under-size particles are of course recycled through the system untilthey have become built up to the desired size. In general the sizes ofscreens 37 and 41 should-be adjusted to take out a 5 relatively narrowout since the amount of sodium monoxide recirculated will run from 19-33times the amount by weight which is withdrawn through pipe 42. Thesystem may be continued in operation until it becomes necessary to shutdown for maintenance.

I claim:

1. The continuous process of preparing sodium monoxide in the form ofnuclear particles of sodium monoxide surrounded by a film of sodiummonoxide, which comprises the step of continuously introducing nuclearparticles of sodium monoxide into a mixing zone, separately introducingmolten metallic sodium into said mixing zone in an amount of about 1% toabout 10% of the weight of said nuclear particles, maintaining thematerials in said mixing zone in a state of continuous agitation and ina temperature range from the melting point of elemental sodium to about250 C., preventing the oxidation of the metallic sodium in said mixingzone by maintaining in said mixing zone an atmosphere inert in relationto metallic sodium and to sodium monoxide at the temperature in saidmixing zone, thereby coating said nuclear particles of sodium monoxidewith a film of metallic sodium, withdrawing particles so coated fromsaid mixing zone and introducing them continuously into an oxidizingzone, controlling the temperature of the material in said oxidizing zoneto maintain it within the range of about 130 C. to about 400 C.,continuously introducing into said oxidizing zone an oxidizingatmosphere providing an amount of oxygen substantially greater thanstoichiometrically equivalent to the metallic sodium present, therebyoxidizing the film of metallic sodium surrounding said nuclear particlessubstantially completely to sodium monoxide and continuously withdrawingnuclear particles of sodium monoxide surrounded by a film of sodiummonoxide from said oxidizing zone.

2. Process according to claim 1 in which the material continuouslywithdrawn from said oxidizing zone is divided into at least twoportions, including a portion serving as the process product and aportion which is recycled to said mixing zone.

References Cited in the file of this patent UNITED STATES PATENTS1,685,520 Carveth Sept. 25, 1928 2,279,088 Gilbert Apr. 7, 1942

1. THE CONTINUOUS PROCESS OF PREPARING SODIUM MONOXIDE IN THE FORM OFNUCLEAR PARTICLES OF SODIUM MONOXIDE SURROUNDED BY A FILM OF SODIUMMONOXIDE, WHICH COMPRISES THE STEP OF CONTINUOUSLY INTRODUCING NUCLEARPARTICLES OF SODIUM MONOXIDE INTO A MIXING ZONE, SEPARATELY INTRODUCINGMOLTEN METALLIC SODIUM INTO SAID MIXING ZONE IN AN AMOUNT OF ABOUT 1% TOABOUT 10% OF THE WEIGHT OF SAID NUCLEAR PARTICLES, MAINTAINING THEMATERIALS IN SAID MIXING ZONE IN A STATE OF CONTINUJOUS AGITATION AND INA TEMPERATURE RANGE FROM THE MELTING POINT OF ELEMENTAL SODIUM TO ABOUT250*C., PREVENTING THE OXIDATION OF THE METALLIC SODIUM IN SAID MIXINGZONE BY MAINTAINING IN SAID MIXING ZONE AN ATMOSPHERE INERT IN RELATIONTO METALLIC SODIUM AND TO SODIUM MONOXIDE AT THE TEMPERATURE IN SAIDMIXING ZONE, THEREBY COATING SAID NUCLEAR PARTICLES OF SODIUM MONOXIDEWITH A FILM OF METALLIC SODIUM, WITHDRAWING PARTICLES SO COATED FROMSAID MIXING ZONE AND INTRODUCING THEM CONTINUOUSLY INTO AN OXIDIZINGZONE, CONTROLLING THE TEMPERATURE OF THE MATERIAL IN SAID OXIDIZING ZONETO MAINTAIN IT WITHIN THE RANGE OF ABOUT 130*C. TO ABOUT 400*C.,CONTINUOUSLY INTRODUCING INTO SAID OXIDIZING ZONE AN OXIDIZINGATMOSPHERE PROVILDING AN AMOUNT OF OXYGEN SUBSTANTIALLY GREATER THANSTOICHIOMETRICALLY EQUIVALENT TO THE METALLIC SODIUM PRESENT, THEREBYOXIDIZING THE FILM OF METALLIC SODIUM SURROUNDING SAID NUCLEAR PARTICLESSUBSTANTIALLY COMPLETELY TO SODIUM MONOXIDE AND CATINUOUSLY WITHDRAWINGNUCLEAR PARTICLES OF SODIUM MONOXIDE SURROUNDED BY A FILM OF SODIUMMONOXIDE FROM SAID OXIDIZING ZONE.